Ion implantation is a process of introducing dopants or impurities into a substrate via bombardment. In semiconductor manufacturing, the dopants are introduced to alter electrical, optical, or mechanical properties. For example, dopants may be introduced into an intrinsic semiconductor substrate to alter the type and level of conductivity of the substrate. In manufacturing an integrated circuit (IC), a precise doping profile provides improved IC performance. To achieve a desired doping profile, one or more dopants may be implanted in the form of ions in various doses and various energy levels.
A conventional ion implantation system may comprise an ion source and a series of beam-line components. The ion source may comprise a chamber where desired ions are generated. The ion source may also comprise a power source and an extraction electrode assembly disposed near the chamber. The beam-line components, may include, for example, a mass analyzer, a first acceleration or deceleration stage, a collimator, and a second acceleration or deceleration stage. Much like a series of optical lenses for manipulating a light beam, the beam-line components can filter, focus, and manipulate ions or ion beam having desired species, shape, energy, and other qualities. The ion beam passes through the beam-line components and may be directed toward a substrate mounted on a platen or clamp. The substrate may be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a roplat.
The ion implanter system generates a stable, well-defined ion beam for a variety of different ion species and extraction voltages to desirably operate the ion source for extended periods of time, while avoiding the need for maintenance or repair. After several hours of normal operation using source gases (such as AsH3, PH3, BF3, and other species), beam constituents eventually create deposits on beam optics. Beam optics within a line-of-sight of the wafer also become coated with residues from the wafer, including Si and photoresist compounds. These residues build up on the beam-line components, causing spikes in the DC potentials during normal operation (e.g., in the case of electrically biased components) and eventually flake off, causing an increased likelihood of particulate contamination on the wafer.
Effectiveness of plasma etching and deposition in electronic device fabrication is reduced by contamination problems. Particulate contamination can result in device failure, poor film quality, changes in material resistivity, and impurity permeation. Further, as device dimensions are reduced, tighter control of the etching profile translates to ever more stringent restrictions on the allowable particle contamination number, density and size.
Furthermore, the effects of particulate contamination can be magnified when selective plasma etching processes are used. Certain plasma etching processes rely on a combination of feed gases and etching conditions to selectively etch material surfaces on the wafer. The chemical formation of particulates, etching at a slow rate in these highly selective plasmas, results in micromasking, or an irregular surface often referred to as “grass”. This spike or hill of unreacted material may also degrade the device performance and reduce process yield.